1. Field of the Invention
The present invention relates to modular bend stiffeners, for example to modular bend stiffeners suitable for cables and pipes where they are anchored for avoiding damage due to stresses experienced by the cable and pipes as they flex and move in operation. Moreover, the present method concerns methods of installing aforementioned modular bend stiffeners onto cables and pipes.
2. Description of the Related Art
Bend stiffeners are conventionally employed for end terminations of cables and/or pipes. For example, bend stiffeners are employed on end terminations of cables hanging in operation from tension leg platforms (TLP), floating production vessels (FPSO), offshore wind turbines, offshore wave energy plant and so forth. These cables are subjected in operation to dynamic motions which cause cable tension and bending curvature, potentially resulting in eventual cable damage unless cable stiffeners are employed. Thus, cable stiffeners have a purpose to distribute such curvature due to dynamic motions along a length of cables so that a maximum stress due to bending is below a damage threshold for the cables.
A conventional bend stiffener is illustrated in FIG. 1 and indicated generally by 10. The stiffener 10 is fabricated from a robust flexible inert material, for example rubber, polyurethane, and is often of a tapered form with a central axial passage 20 for accommodating at least one pipe and/or cable 30. The tapered form renders the conventional bend stiffener 10 stiffest at its widest end 40, namely its proximate end, and most flexible at its thinnest end 50, namely its distal end. The bend stiffener 10 is attached to a major stationary component 60, for example an offshore platform, at its widest end 40, and the thinnest end is free to move as a distal portion of the bend stiffener 10. Thus, the conventional bend stiffener 10 is often a massive conical component manufactured from polyurethane plastics material.
Relatively few contemporary manufacturers have production facilities suitable for producing the conventional bend stiffener 10. Moreover, the bend stiffener 10 must be assembled to cables and terminations before they are loaded onto an installation vessel for being transported to theft location of eventual use. When cables are loaded onto drums, theft associated bend stiffeners require that larger drums have to be used which increases cost. There are length restrictions for conventional contemporary bend stiffeners on account of suppliers manufacturing equipment limitation.
Various types of bend stiffeners have been reported in earlier literature. For example, in a published United Kingdom patent application no. GB 2 428 760 A (Trelleborg CRP Ltd.), there is described an articulated centralizer for a pipe or other elongate member which is formed from a plurality of tubular bodies. Each body includes an axial through passage, and a plurality of such bodies is operable to be connected end-to-end to form a continuous elongate passageway. Each of the tubular bodies has a female-type connector portion at a first end thereof, and a male type connector portion at a second end thereof remote from the first end, wherein the male-type portion and the female-type portion are operable to mate with a degree of longitudinal and/or angular play. The centralizer includes securing means implemented as a mounting flange for fixing the centralizer with respect to a J-tube through which the centralizer is to pass. The centralizer is operable to centralize the elongate member in the J-tube and to maintain an allowable minimum bending radius for protecting the elongate member from bending damage and also reduce subsequent abrasion damage to the elongate member. The tubular bodies are beneficially manufactured from a polyurethane elastomer material. Moreover, the portions have mutually similar size.
In a published international POT patent application no. WO 2006/033579 (Marine Subsea Group AS), there is described a bend stiffener which is adapted to surround an end portion of an elongate cylindrical object, for example a flexible pipe or a cable, extending from a subsea installation to a surface vessel. The bend stiffener is connected to an end piece or end flange of the elongate object at a connection to the vessel. The bend stiffener is provided by a plurality of inner cylindrical clamps and associated outer cylindrical clamps which surround the elongate object when installed. Moreover, the clamps include longitudinal grooves for receiving spring rods therebetween. The spring rods are disposed in operation parallel to the elongate cylindrical object so that the elongate cylindrical object is protected by the spring rods from external damage, and the spring rods also limit a radius of curvature of the elongate object when it is subject to lateral stresses. The spring rods exhibit a substantially similar compliance along their length, although axial distances between the clamps along the elongate object are potentially susceptible to being varied.
In a published international PCT patent application no. WO 01/75262 A1, there is described a bend stiffener suitable for use in association with a riser in offshore oil and gas recovery. The stiffener comprises a tubular member adapted to engage the riser, wherein the riser comprises a plurality of parts which are mutually coupled together in use for providing the tubular member. The parts are manufactured from polyurethane material. Moreover, the tubular member is of a conical tapered form from its first end to its second end, but with a central axial passage of substantially constant diameter along the stiffener.
In a published European patent application no. EP 0859 182 A2, there is described a bend stiffener implemented to include an elongate frusto-conical polyurethane body which is moulded around an adhered metal connecting sleeve at one end. The elongate body has an elongate central axial aperture for receiving an end portion of a pipe. Moreover, the body is formed of several pre-formed sections which are secured together in operation to form the frusto-conical body. It is alleged that it is easier to manufacture the bend stiffener because the sections are smaller than the entire frusto-conical body itself, thereby shortening solidifying time during manufacture and rendering transport easier in comparison to transporting the frusto-conical body if it were manufactured as a unitary component.
Many of the aforementioned bend stiffeners are manufactured from relatively massive polyurethane components which are difficult to manufacture, such that there are relatively few commercial vendors. Moreover, many of the bend stiffeners are designed in such a manner that the bend stiffeners need to be installed onto cables or pipes before installation occurs. Such issues represent a major technical problem experience with contemporary bend stiffeners.